Plastic mulch is an essential and widely used method in various agricultural practices. In field crop and vegetable production there is an increasing use of soil mulching with plastic films. Soil mulching during cold seasons results in elevated soil temperatures and enhanced seedling emergence, plant growth and crop production. Summer crops such as corn, peanuts and cotton cannot be planted early in the season. Therefore planting is delayed to late spring and growth season is extended to late fall. Therefore, the crop is exposed to severe damage by early rains. A method for increasing soil temperature allows planting early in the season and increasing the potential of crop yield. Soil mulch during crop growth provides various benefits. Mulch can be used for the purpose of repelling insects. Silver or yellow mulches are used to repel aphids and to prevent damage from their feeding and from transmission of viruses. White film can be used to reduce soil temperature during hot periods. Mulch can also provide protection from rot of fruit touching the soil, such as tomato, melon and watermelon.
Soil solarization is a method for soil disinfection consisting of covering the soil with transparent plastic films during the summer. The soil is heated for a period of a few weeks thus effectively controlling various soilborne pests. Applying plastic films for soil mulch is complicated. It requires special mulching equipment and involves special procedures. The film's edges should be buried to hold the film in place, and in continuous mulch the sheets are glued together. It is not possible to change the mulching pattern while working and capacity of area coverage is limited. When applying to a planted field, the sheets have to be perforated or be removed immediately after emergence to allow seedling growth. Plastic mulches have to be removed from the fields during or at the end of crop growth. Plastic removal is expensive and requires intensive labor. Plastic residues are often left in the field causing problems to agricultural practices, machinery and future crops. The present invention overcomes these disadvantages and provides a new method for soil mulching by spraying latex-based polymers. Although patents related to spraying polymer dispersions were previously issued, these patents focused on polymer type and formulation, composition and use and all of these patents consider the use of available commercial sprays which are not appropriate for creating a membrane film at low rates of spray. Therefore, the actual volume of spray required for effective cover is between 200 to 2000 ml/m.sup.2, which is very high.
U.S. Pat. No. 2,961,799 discloses a method for treating soil to prevent erosion. The method involves applying to the soil a composition comprising about 0.5 to 5, preferably about 2 to 4, weight percent of water insoluble rubber and 0.005 to 0.5, preferably about 0.05 to 0.15, weight percent of a counter penetrant at a rate providing about 0.25 to 5 ounces per square yard. The counter penetrant is used to prevent the compound from significantly penetrating the top layer of the soil. The type of sprayer used is not important as long as it enables applying an even coating with relatively easy control.
British patent 1,007,671 discloses a process for controlling soil erosion. The process comprises applying to the soil a latex of an oil extended rubber. The rubber latex may be extended with 50 to 1000 parts by weight of oil per 100 parts by weight of rubber. The latex is applied at a rate providing about 40 to 300 grams per square meter. The latex is applied at a solids' content of about 5 to 30 percent.
U.S. Pat. No. 4,705,816 comprises a significantly higher solids level than that in first U.S. patent mentioned. The higher solid level is accomplished by the addition of filler compound. This formulation rapidly dries to form a crust on the soil surface. Commercially available spraying equipment may be used in this invention as in the other inventions mentioned.
Application of polymer dispersion for soil mulch is not simple and cannot be regarded as spraying other chemicals, such as herbicides. Soil surface is not smooth and is porous. Soil surface should be smooth and compact to carry the spray film and to prevent leaching of the dispersion. The latex dispersion is viscous and flows through the sprayers in a different pattern than common liquid sprays. Therefore, the design of commercially available sprayers is not appropriate for the purpose of a uniform film at rates as low as 30 gr/m.sup.2.
The above mentioned patents refer to the use of commercially available sprays for application of the dispersion. In practice, all these inventions must use a relatively high dosage of spray to accomplish a uniform and appropriate coat, for the desired agricultural demands.
The present invention provides a novel method for applying liquid plastic polymers to soil surfaces in order to form a continuous membrane film. This spray mulch is for the purpose particularly of enhancing crop production, disinfestation of soil by solarization and prevention of soil erosion. The present method for spray application of polymer mulch offers a feasible and cost effective alternative to plastic mulch. The procedure used in the present invention results in dramatic reduction of the volume of the spray required.
The polymer according to the present invention may be applied by spraying the desired quantity. The sprayer of the present invention consists of spraying units and placement to provide the appropriate droplet size and multiple overlapping of the spray at each spot on the soil, in order to form a uniform continuous film on the non smooth pattern of soil surface. The flexibility of nozzle type to be used according to the present invention, gives the advantage of adjusting boom height according to field conditions and weather.
As used in this specification, the term "soil mulch" includes applying coats to cover the soil of trays of flowers or vegetables grown in greenhouses, fields such as in growing cereals including corn and sorghum in vegetable and fruit farms, outdoor nurseries for trees, shrubs and plants and also various agricultural practices, including raised beds, flat areas and others. The term--"Applying liquid polymer to soil surface in order to form a continuous membrane film" as used in this specification, means that when the compound is applied at a desired rate to the surface of soil or of an artificial medium, it will form a flexible film according to polymer formulation and characteristics. This film provides a porous membrane that can withstand normal agricultural practices expected during crop growth. The level of permeability of the membrane film can be adjusted by the volume of compound which is sprayed.
As used in this specification, the term "appropriate polymer" refers to any polymer that can be used to create plastic film.
"Diluted formulation of the polymer", unless otherwise indicated, refers to any percent of polymer, though, in the primer coating, 8% of polymer in the formulation is preferable, being the most economical.